Nikon Prostaff 3i Rangefinder - Ultra-compact and lightweight the Prostaff 3i fits in a pocket or pack, and can be worn on a belt without interfering with your shot. Single button operation for fast, easy measurements. Automatically powers down after 8 seconds to reduce battery use. Nikon's legendary optics and proprietary anti-reflective coatings offer high-resolution images in most lighting conditions. Runs on one CR2 lithium battery (included). Rainproof and fogproof for use in any weather.